Transformer with a fuse

ABSTRACT

A plastic bobbin-like body for a fused coil, such as a primary winding of a power transformer, is provided with end flanges. A fuse-mounting groove is provided on the outside of a thickened section of one flange. A fuse strip made of a metal having a suitably low melting point is placed in the groove and is held in position by barbed connecting lugs inserted into passages which run parallel to the flange walls to the bottom of the groove. The coil is connected in series with the fuse through the lugs. A large cavity around the center of the groove allows liquid metal to quickly fall away from the fuse when excessive current heats the fuse to its melting temperature. Alternatively, the lugs may be provided with tabs which project out of the thickened section. The tabs are then rolled over the fuse mounted on the outside of the thickened section.

United States Patent Weyrich et al. [4 1 Sept. 12, 1972 TRANSFORMER WITH A FUSE FOREIGN PATENTS OR APPLICATIONS [72] inventors: Arthur G. Weyrich, Rolling 406,357 1/1910 France ..317/15 Meadows; Richard R. Bertrand,

Skokie; Edwin D. Karinski, Chicago, all of ill. [73] Assignee: Certron Corporation, Anaheim,

Calif. 221 Filed: April 15, 1971 [21] Appl.No.: 134,340

[52] U.S. Cl. ..317/15, 336/105, 336/192, 336/198 [51] lnt.CI. ..H02h 7/04 [58] Field of Search ..336/192, 198, 105; 317/15, 317/157.6

[56] References Cited UNITED STATES PATENTS 3,359,520 12/1967 Foerster ..336/192 3,461,413 8/1969 Randolph ..336/192X 3,553,621 l/l971 Lane ..336/192 3,585,450 6/1971 Lane ..317/15 Primary Examiner-E. A. Goldberg Attorney-Lindenberg, Freilich & Wasserman [57] ABSTRACT A plastic bobbin-like body for a fused coil, such as a primary winding of a power transformer, is provided with end flanges. A fuse-mounting groove is provided on the outside of a thickened section of one flange. A fuse strip made of a metal having a suitably low melting point is placed in the groove and is held in position by barbed connecting lugs inserted into passages which run parallel to the flange walls to the bottom of the groove. The coil is connected in series with the fuse through the lugs. A large cavity around the center of the groove allows liquid metal to quickly fall away from the fuse when excessive current heats the fuse to its melting temperature. Alternatively, the lugs may be provided with tabs which project out of the thickened section. The tabs are then rolled over the fuse mounted on the outside of the thickened section.

9 Claims, 12 Drawing Figures TRANSFORMER WITH A FUSE BACKGROUND OF THE INVENTION This invention relates to fused coils wound on a bobbin-like body, and more particularly to such a body having an integral means for holding a fuse and for connecting a coil wound on the form in series with the fuse.

In the past fused coils, such as in power transformers, have been wound on a form and connected to a fuse on a separate connector board. That fuse-connector board then had to be accommodated in packaging the wound coil. It would be desirable to provide fused coils without a separate connector board.

SUMMARY OF THE INVENTION In accordance with the present invention, a coil is wound on a body of electrical insulating material having an axis around which the coil is wound. The form has a thickened section with a surface normal to that axis and with sufficient area to accommodate a groove into which a fuse of the metal-strip type is placed. The fuse is secured in place by a pair of barbed connecting lugs inserted into passages running through the body in a direction parallel to the aforesaid surface area and leading to the ends of the groove at a level near the bottom of the groove to make contact with the fuse wire by butting the end of the terminal against the fuse wire, or by overriding the fuse wire. Alternatively, the lugs may be provided with tabs which project out of the thickened section. The tabs are then rolled over the fuse mounted on the outside of the thickened section. The lug passages are sufficiently narrow to engage the barbs of the connecting lugs, and the lugs are sufficiently long to leave a substantial portion protruding in order to connect one end of the coil to one end of the fuse, and an external connecting lead to the other end of the fuse.

For a fused transformer, the body is tubular and has a flange at each end, one providing the surface area for the fuse or a fuse groove. Each coil wound directly on the same body is separated from any other coil wound on the same body by an additional flange. A transformer core is inserted through the center of the tubular body and around all of the coils on at least one side to form a closed magnetic loop. In a fused power transformer of the type having the coils covered on all sides by metal adapted to be connected to earth, the leads of the fused coil pass through an aperture in the cover. Leads from other coils in the transformer are adapted to be connected to external circuits by conventional means.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an isometric view of a bobbin-like body for winding coils of a fused transformer in accordance with the present invention.

FIG. 2 is a schematic diagram of a fused transformer to be provided on the body of FIG. 1.

FIG. 3 is a sectional view of the body of FIG. 1 taken along the line 3-3 with the two transformer coils wound in place.

FIG. 4 is a sectional view of FIG. 3 taken along a line 4-4 in FIG. 3.

FIG. 5 is a sectional view taken along a line 5-5 of FIG. 4.

FIG. 6 illustrates a prior art technique for providing coils of a fused transformer on a form.

FIG. 7 shows an exploded isometric view of a complete transformer fused in accordance with the present invention.

FIG. 8 is a sectional view corresponding to FIG. 4 of an alternative embodiment of the present invention.

FIG. 9 is an end view of a bobbin-like body with a fused coil in accordance with an alternative embodiment of the present invention.

FIG. 10 is a side view of FIG. 9.

FIG. 11 is a sectional view of FIG. 9 along a line 11- 11 before a fuse of the metal-strip type is added to the assembly.

FIG. 12 shows the structure of FIG. 1 1 after a fuse of the metal-strip type is added to the assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a bobbin-like body 10 for a fused transformer is shown comprising an elongated tubular section 11 having end flanges 12 and 13, and a center flange 14. The coils of the transformer are wound directly on the tubular section 11, each coil being wound between a separate pair of flanges. A thickened section or block 15 is provided on the outside of the flange 13 either as a separate piece cemented or fused on the flange or as a unitary section of the flange, and is adapted to hold a fuse of the metalstrip type in such a manner that, in accordance with the present invention, the coil wound between the flanges l3 and 14 may be connected in series with the fuse through connecting lugs 16 and 17. Once the coils have been wound and the fuse has been connected in series through the lugs 16 and 17, a laminated core is inserted in the tubular section 11 in a conventional manner to form the circuit illustrated schematically in FIG. 2 consisting of coils 20 and 21, a core 22 and a fuse 23. In a fused power transformer, the coil 20 connected to the fuse 23 is generally the primary winding of the transformer. Accordingly, the free ends of the coil 20 and the fuse 23 are adapted to be connected to a power source with heavily insulated wires.

The manner in which the fuse 23 is held in the thickened section 15 for series connection with the coil 20 by connecting lugs 16 and 17 will now be described with reference to FIGS. 3 and 4. A groove 30 is provided in the block 15 to a depth substantially half the thickness of the block 15 as shown in the sectional view of FIG. 4 taken along the line 5-5 in FIG. 3. Passages are provided from the top of the block 15 to the groove 30 in a plane parallel to the face of the block 15. When the lugs 16 and 17 are inserted into the passages, the ends of the lugs abut the fuse 23 and hold it in place in the groove 30. In that manner pressure from the lugs press the fuse against a wall of the groove 30. Friction between the lugs 16 and 17 and the walls of the passages 31 and 32 is enhanced by barbs on the lugs.

A cavity 33 is provided in the block 15 at the center of the groove 30, and to a greater depth, in order to allow liquid metal from the fuse to flow away and thereby open the current path between the lugs 16 and 17 quickly when excessive current is conducted through the fuse. The center of the fuse will be the first to melt because the lugs 16 and 17 connected to the ends will function asheat sinks, thereby keeping the ends below melting temperature while the center is being heated to the melting temperature.

The bobbin-like body is cast from a suitable plastic material. The block is also formed out of the same plastic material, preferably by casting as a unitary part or thickened section of the flange. Still another possibility is to cast the flange 13 of sufficient thickness to accommodate the slot 30 and the passages 31 and 32 for the fuse 23 and the lugs 16 and 17, respectively. The block 15 would then appear only as a section of the flange 13 selected for the slot 30 and the passages 31 and 32. The plastic material serves to electrically insulate the lugs 16 and 17 and the fuse 23 as well as the coils 20 and 21, although the coils do not require that the body 10 be cast from an insulating material because the wire used for the coils is already insulated.

It should be noted that the body 10 has a tubular section 11 which is rectangular rather than circular in cross section only for the purpose of receiving a core which has a rectangular cross section. If the fused coil is to be provided without a core such as a choke coil, the section 11 may be solid rather than tubular, and may in some instances be formed without any flanges. In that event, the slot 30, and passages 31 and 32, would be provided directly on the end of the solid section 1 1, rather than on a flange at the end.

Referring now to FIG. 5, the present invention as applied to a fused transformer is shown in a sectional view taken along a line 55 of FIG. 1 with the coils 20 and 21 in place, but without a transformer core and without any enclosure or cover. The prior art technique for accomplishing the same thing in forming a fused transformer is shown in FIG. 6 with corresponding reference numerals distinguished by a prime in order to facilitate comparison of the prior art technique with the present invention.

The prior art technique consist of employing a tubular form 1 l on which layers of the coils are wound, one layer at a time for a given coil, each layer being covered with paper to separate it from the next layer. First one coil is wound and then the other. Here the first coil 20 is connected to a fuse 23' through a tab 17' riveted to a board 15' of insulating material, the rivet serving not only to connect the lug 17 to the fuse 23' but also to secure both to the board 15'. A lug 16' is similarly connected to the other end of the fuse 23' by riveting to the board 15. Still another lug 18' is riveted to the board 15' to provide means for connecting the other end of the coil 20 to an outside circuit. The board 15' is laid over the paper covering the last layer of turns of the coil 21 in the dotted line position.

A comparison of FIGS. 5 and 6 shows that the structure of FIG. 1 which comprises a bobbin-like body with an integral fuse-holding structure provides distinct assembly advantages. First, it is easier to wind the coils separated by flanges than it is to wind coils separated by layers of paper. Second, it is easier to install a fuse and to connect the fuse in series with one of the coils. And third, no further effort is required in regard to the fused-connecting structure before a transformer core and enclosure or cover is provided, except bending the lugs 16 and 17 over the coil 20 to avoid contact with a metal cover.

FIG. 7 illustrates in an exploded isometric view the manner in which a transformer core 40 is added to complete the assembly of a fused transformer in accordance with the present invention. The core 40 consists of a first part 41 made of laminated iron sheets in the form of an E and a second part 42 made of laminated iron sheets in the form of a letter I. The center leg of the E-part 41 is inserted into the tubular section on which the coils 20 and 21 are wound. The I- part 42 is then placed over the open ends of E-part 41 to complete two magnetic circuit loops through the center of the coils 21 and 22 and around both sides. The two parts of the core are held together in a conventional manner, such as by welded joints 43 and 44. Any other technique for securely holding the l-part 42 against the E-part 41 will suffice, such as simply bolting together transformer covers 45 and 46 with the parts 41 and 42 in place.

The covers 45 and 46 are normally made of metal so that when they are provided they form an electromagnetic shield around the transformer coils. However, it should be understood that either one or both covers may be omitted in some applications.

Before the covers 45 and 46 are bolted together to complete the assembly, the ends of the secondary winding (coil 21) are soldered to connectors. 47 and 48 (which pass through the cover 46) for connections to external circuits. Both of the connectors 47 and 48 are electrically isolated from the metal cover 46 in a conventional manner, such as by mounting the connectors in a panel 49 of nonconductive material that is set into a large aperture in the cover 46.

One end of the primary winding (coil 20) is connected to the lug 17. The other lug 16 at the other free end of the fuse is connected to a heavily insulated conductor 50. The other free end of the primary winding is connected to a second heavily insulated wire 51 at an insulated junction 52. Both of the wires 50 and 51 are passed through an aperture 53 in the cover 45. A rubber grommet 54 prevents the insulation of the wires 50 and 51 from being frayed. The lugs 16 and 17 may be bent over the coil 20, but not in contact with any of the turns in the coil 20, to avoid possible contact with the cover 45. To assure that the heavily insulated wires 50 and 51 are not pulled loose from their connection within the cover 45, some measure may be taken to keep all of the slack from being pulled out of the cover 45, such as tying a knot in the leads 50 and 51 inside the cover.

An alternative embodiment of the present invention will now be described with reference to FIG. 8. It is essentially the same as the embodiment just described, but differs in a manner which can best be appreciated by comparison of FIG. 8 with FIG. 4. To facilitate comparison, the same reference numerals are employed, except for the groove 30' distinguished by a prime over the reference numeral.

The difference between this embodiment and that of FIG. 4 is that the groove 30' is made to a depth sufficient for the fuse 23 to be behind the passages, but in communication with the passages, such as the passage 31. Once the fuse 23 is in place, the lugs are inserted to a sufficient depth in their passages to allow them to override the fuse 23, as shown for the lug 16. This arrangement provides a more positive way of securing the fuse in place.

Still another embodiment will now be described with reference to FIGS. 9 to 12, again using the same reference numerals for elements common to the first embodiment. The difference between this embodiment and previously described embodiments is that no groove is provided for the fuse 23 in the thickened section or block 15. Instead, slots 60 and 61 are provided through which tabs 62 and 63 from the lugs protrude, as shown for the lug 16 in FIG. 11. Once the fuse 23 is placed in the position shown in FIG. 9, the tabs 62 and 63 are rolled over the fuse 23, as shown for the tab 62 in FIG. 12. FIG. shows a side view of a bobbin with the fuse 23 secured in place.

A third lug 65 shown in the end view of FIG. 9 may be similarly mounted in a passage like the lugs 16 and 17, except without a front slot. The third lug serves as terminal post for connecting a lead 50 to one end of a coil while the lug 16 serves as a terminal post for connecting a lead 50 to one end of a coil and the lug 16 serves as a terminal post for connecting the other lead 51 to the fuse 23, which is in turn connected to the other end of the coil through the lug 17.

Although particular embodiments have been illustrated and described herein, it is recognized that modifications and variations may readily occur to those skilled in the art. Consequently, it is intended that the claims be interpreted to cover such modifications and variations.

What is claimed is:

l. A form for a fused coil comprising:

a body of electrical insulating material having a longitudinal axis for carrying a coil wound around said longitudinal axis, said body having an end section with a surface normal to said axis,

g a pair of passages in said body running in a direction substantially parallel to the surface of said end section,

a strip of metal having two ends, said strip of metal being selected both as to composition and form to heat to a melting temperature in response to current at a predetermined level conducted from one end thereof to the other end,

a pair of connecting lugs, one lug inserted into one of said passages, and the other lug inserted into the other of said passages, each of said lugs being sufficiently long to have a substantial portion protruding from said body, and

means for securing said metal strip in electrical contact with said lugs, one lug at each end of said metal strip whereby one end of a coil wound on said body may be connected directly to one tab thereby placing said metal strips as a fuse in series between the other end of said coil and the other tab, said means comprising a groove formed in said end section through said end surface, wherein each of said pair of passages in said body is in communication with a different end of said groove at a level near the bottom of said groove, said strip of metal being placed in said groove, and said pair of connecting lugs being inserted sufficiently into said passages to engage said metal strip and secure said metal strip in said groove.

2. The combination of claim 2 including a cavity formed in said body around the center of said groove, the depth of said cavity being greater than the depth of said groove.

3. The combination of claim 3 wherein said groove intersects said pair of passages and each of said lugs engages said metal strips by abutting said metal strip in said groove, thereby holding said metal strip in place by pressure of said abutting lugs.

4. The combination of claim 2 wherein said groove is behind said pair of passages relative to said surface and in communication with said passages and each of said lugs engages said metal strip by overriding said metal strip in said groove.

5. The combination of claim 2 wherein said body includes two flanges, a flange on each end.

6. The combination of claim 5 wherein said body is tubular, and one of said flanges at one end of said body provides said section into which said groove and cavity are formed.

7. The combination of claim 6 wherein said body includes a third flange intermediate said end flanges and further includes,

first and second coils wound around said body to form a transformer, each coil being separately wound between a separate pair of flanges, said first coil being wound next to said flange into which said groove is provided, one end of said first coil being connected to one of said lugs, and

a transformer core passing through said tubular form and around both of said coils on at least one side in a closed magnetic circuit.

8. A form for a fused coil comprising a body of electrical insulating material having a longitudinal axis for carrying a coil wound around said longitudinal axis, said body having an end section with a surface normal to said axis,

a pair of passages in said body in a direction substantially parallel to the surface of said end section,

a strip of metal having two ends, said strip of metal being selected both as to composition and form to heat to a melting temperature in response to current at a predetermined level conducted from one end thereof to the other end,

a pair of connecting lugs, one lug inserted into one of said passages, and the other lug inserted into the other of said passages, each of said lugs being sufficiently long to have a substantial portion protruding from said body, and

means for securing said metal strip in electrical contact with said lugs, one lug at each end of said metal strip whereby one end of a coil wound on said body may be connected directly to one tab thereby placing said metal strips as a fuse in series between the other end of said coil and the other tab, said means comprising slots opening said passages to said surface of said end section, and a tab protruding from each of said lugs, each tab being tight around said metal strip laying against said surface of said end section, whereby said tabs hold said metal strip secure against said end surface and provide electrical connection from one lug to the other through said metal strip;

9. The combination of claim 8 wherein said body includes two flanges, a flange on each end, and one of said flanges at one end of said body provides said thickened section into which said lug passages are formed. 

1. A form for a fused coil comprising: a body of electrical insulating material having a longitudinal axis for carrying a coil wound around said longitudinal axis, said body having an end section with a surface normal to said axis, a pair of passages in said body running in a direction substantially parallel to the surface of said end section, a strip of metal having two ends, said strip of metal being selected both as to composition and form to heat to a melting temperature in response to current at a predetermined level conducted from one end thereof to the other end, a pair of connecting lugs, one lug inserted into one of said passages, and the other lug inserted into the other of said passages, each of said lugs being sufficiently long to have a substantial portion protruding from said body, and means for securing said metal strip in electrical contact with said lugs, one lug at each end of said metal strip whereby one end of a coil wound on said body may be connected directly to one tab thereby placing said metal strips as a fuse in series between the other end of said coil and the other tab, said means comprising a groove formed in said end section through said end surface, wherein each of said pair of passages in said body is in communication with a different end of said groove at a level near the bottom of said groove, said strip of metal being placed in said groove, and said pair of connecting lugs being inserted sufficiently into said passages to engage said metal strip and secure said metal strip in said groove.
 2. The combination of claim 2 including a cavity formed in said body around the center of said groove, the depth of said cavity being greater than the depth of said groove.
 3. The combination of claim 3 wherein said groove intersects said pair of passages and each of said lugs engages said metal strips by abutting said metal strip in said groove, thereby holding said metal strip in place by pressure of said abutting lugs.
 4. The combination of claim 2 wherein said groove is behind said pair of passages relative to said surface and in communication with said passages and each of said lugs engages said metal strip by overriding said metal strip in said groove.
 5. The combination of claim 2 wherein said body includes two flanges, a flange on each end.
 6. The combination of claim 5 wherein said body is tubular, and one of said flanges at one end of said body provides said section into which said groove and cavity are formed.
 7. The combination of claim 6 wherein said body includes a third flange intermediate said end flanges and further includes, first and second coils wound around said body to form a transformer, each coil being separately wound between a separate pair of flanges, said first coil being wound next to said flange into which said groove is provided, one end of said first coil being connected to one of said lugs, and a transformer core passing through said tubular form and around both of said coils on at least one side in a closed magnetic circuit.
 8. A form for a fused coil comprising a body of electrical insulating material having a longitudinal axis for carrying a coil wound around said longitudinal axis, said body having an end section with a surface normal to said axis, a pair of passages in said body in a direction substantially parallel to the surface of said end section, a strip of metal having two ends, said strip of metal being selected both as to composition and form to heat to a melting temperature in response to current at a preDetermined level conducted from one end thereof to the other end, a pair of connecting lugs, one lug inserted into one of said passages, and the other lug inserted into the other of said passages, each of said lugs being sufficiently long to have a substantial portion protruding from said body, and means for securing said metal strip in electrical contact with said lugs, one lug at each end of said metal strip whereby one end of a coil wound on said body may be connected directly to one tab thereby placing said metal strips as a fuse in series between the other end of said coil and the other tab, said means comprising slots opening said passages to said surface of said end section, and a tab protruding from each of said lugs, each tab being tight around said metal strip laying against said surface of said end section, whereby said tabs hold said metal strip secure against said end surface and provide electrical connection from one lug to the other through said metal strip.
 9. The combination of claim 8 wherein said body includes two flanges, a flange on each end, and one of said flanges at one end of said body provides said thickened section into which said lug passages are formed. 